The present invention relates to a honing tool which is specifically constructed and used to accurately hone blind bores or holes located in workpieces. A blind bore is a bore that does not go all the way through the workpiece and because of this the tool and method of using the tool must be modified from the more conventional honing tool which rotates and expands as it is stroked and moves back and forth in the workpiece. In the more conventional honing tool, the honing mandrel is expanded by pushing a wedge shaped member against the member or members on which the abrasives are located to move them radially outwardly into engagement with the work surface while also maintaining them in a cylindrical condition. This is not possible with blind holes because with a blind bore the tool can not reciprocate in the ordinary manner and usually must be retracted to enter the bore before the honing operation commences and the expansion of the honing member or mandrel is reversed from the usual method so as to enable a portion of one end of the honing portion to expand outwardly more than the other portions thereof to enable the mandrel to hone a cylindrical surface to the desired diameter and to do so over the entire length of the blind hole.
Since a blind bore does not go all the way through the part or workpiece, the honing or finishing of a blind bore is usually relatively difficult because the honing tool cannot pass all the way through the bore or hole and beyond and therefore stroking in the usual way is difficult or impossible. Typically, the obstructed end of the work piece usually has some type of relief or undercut area. The size and length of the relief area is usually not necessarily critical but the length of the undercut can be important because the length determines the amount of over stroke which can be accomplished when attempting to finish a blind bore to the same final size along the full length and with minimum taper. In the past, the honing of blind holes often used a single stroke procedure, but even this would produce some inaccuracy and would often require that the bore be rehoned by a second, third or more stroking without producing a taper of some kind. When honing with a tool that strokes back and forth, the stroking of the tool beyond the end of the workpiece bore into the relief area is usually required if the operation is to be successful and accurate. If there is not adequate relief for a long enough over stroke at the closed end of the bore, a barrel shaped bore often occurs in the surface being honed and this will produce a bore that is not cylindrical along its full length.
When using a single stroke honing tool, the tool is generally tapered for removing the material. The nature of this type of tool typically makes the final size of the bore smaller at the bottom or closed end as compared to the rest of the bore length. This is true because the size of the relief is usually not large enough to allow the bottom or closed end of the workpiece bore to be properly honed to its desired final size.
The present invention is directed to a honing tool and method of use specifically designed to hone blind bores to the same desired final size or diameter along the entire length of the bore surface. In this case, the tool is designed so as to be operated in a reverse manner as compared to a typical honing tool. More specifically, the present tool is designed so as to be positioned within the blind bore to be honed in its retracted condition, that is, at a dimension that is less than the dimension of the bore, and is then expanded while at or near the bottom or closed end of the blind bore to a particular size and pulled or drawn out of the blind bore while rotating at a controlled feed rate to achieve the final diameter which is uniform along the length of the bore. Depending upon the amount of material to be removed in this manner, this honing operation can be accomplished with a single pass or with multiple passes as will be described later.
The present tool includes an elongated substantially tubular member having an opening or passageway extending the entire length thereof and adaptable for insertably receiving an elongated expander member or wedge positioned for axial movement therein. The tubular member includes inner and outer surfaces, at least a portion of the outer surface at one end including an abrasive material thereon for accomplishing the honing operation, while the inner surface of at least that portion of the tool that corresponds to the outer abrasive portion is conically tapered over substantially the entire length of the abrasive portion as will be explained later and shown in the drawings. In contrast with the conventional honing devices the expander member or wedge assembly in the present construction has an outer surface which is conically tapered over at least a portion of its length at or near the same taper rate as the conical taper associated with that portion of the inner surface of the tubular honing member where the outer abrasive surface is located. This means that when the expander member is positioned within the tubular member, the tapered outer surface of the expander member can move into surface-to-surface contact with the tapered inner surface of the tubular honing member.
The tubular honing member also includes one or more slots extending from the end thereof along and beyond the abrasive portion of said member to permit expanding and contracting the abrasive portion of the honing member when the wedge is advanced or retracted axially therein. The present tool also includes means associated with one end portion thereof for mounting the tool to a rotatable member or spindle on a honing machine so that the tool can be rotated about its axis of rotation during a honing operation. In similar manner, the expander member or wedge assembly engages and is axially moved by means on the honing machine which are operable to move the wedge axially to change the diameter of the outer surface of the abrasive portion of the honing member. The abrasive portion of the present tool can have any desired pattern or configuration and, importantly, includes at least one lead-in or cutting taper near the lead end which is designed to remove most of the material during a particular honing stroke. The present honing tool is constructed to be retracted before insertion into the blind bore, and thereafter is expanded and pulled back through the hole while rotating. The cutting taper is usually slight and located at or near the free end of the abrasive portion of the tool. In other words, the cutting taper is such that the largest diameter is at or adjacent the free end of the abrasive portion of the tool as is shown in the accompanying drawings. This is different from conventional honing tools where the honing portion is cylindrical over its entire length.
The present tool may include a plurality of lead-in tapers such as first and second tapers, the second taper being positioned and located immediately following the first taper and being of a taper rate which is less than the taper rate of the first taper. The second or later taper portion can be followed by a substantially cylindrical abrasive portion, and the cylindrical abrasive portion can be followed by a reverse taper portion if desired. Any combination of tapers and cylindrical honing sections can be utilized in a particular tool depending upon the particular application.
Furthermore, if there are a plurality of slots associated with the present honing tool, this enables it to more uniformly expand and contract and the slots may take several different forms including being of straight or helical configurations. The same is true of the honing surfaces which may take helical, straight or other shapes that extend around the outer surface of the honing portion of the tool. The use of nonlinear grooves or flutes in the abrasive portions of the honing member also provide means for the circulation of honing oil or coolant during the honing operation which often times is an advantage. The tool needs to be formed of a relatively elastic material so that it can retract when the wedge is withdrawn and can expand when the wedge is advanced.
The method for using the subject tool is also new and enables the machine operator to manually or otherwise program the honing of blind bores by positioning the mandrel in its retracted condition so that it can enter the unhoned bore without touching or rubbing on the wall of the bore during entry. The tool is then moved to adjacent to the bottom or closed end of the bore and once properly positioned, the tool is expanded and rotated at a controlled rate. The amount of time that the tool remains in the bottom or closed end position before moving can be used to allow the material at the closed end of the bore to be removed by the tool before vertical or axial movement of the tool begins. The expanded rotating tool is then pulled out of the workpiece at an appropriate rate which will ensure that the workpiece bore is honed to the same size over its entire length. If the amount of material removed during a single pass of the tool through the bore is less than the total amount of material which must be removed from the bore to reach the desired size this process can be repeated with the tool expanded out further for each succeeding pass until the desired final dimension is reached. The entire sequence can be programmed so as to allow the operator to move the tool to any desired position in the bore at different rates and different numbers of times in order to bring the workpiece surface up to the desired size. The expanding and contracting of the tool can take place at different rates and the speed of rotation of the tool can also be varied depending upon the nature of the abrasive material used and the material of the surface being honed. Typical abrasives include plated diamond and borozon particles and various metal bonded abrasives. In a computer operated machine, the starting and final diameters can be preprogrammed as well as the other operating conditions such as the length of the bore, the material from which the workpiece is made, and the type of abrasive material that is being used and other parameters as will be described. The present method will size and finish the blind bores to precise tolerances without the tolerance levels degrading the even wear of the tool. This then is a honing method that does not fail because of uneven wear of the tool.
It is a principal object of the present invention to provide means to enable a honing machine to be used to accurately hone blind bores.
Another object of the present invention is to enable existing honing machines to be programmed to hone blind bores.
Another object is to enable existing honing machines to be modified to enable them to hone in blind bores.
Another object is to enable accurately honing blind bores by inserting a retracted honing mandrel into the bore being honed and expanding it when fully inserted so that when it is drawn out of the bore while rotating, it will hone the surface to the same dimension over its full length.
Another object is to teach a novel method for honing blind bores which can make use of some existing technology.
These and other objects and advantages of the present invention will become apparent after considering the following detailed description of the present invention in connection with the accompanying drawings.
The present invention relates to a novel apparatus which can be used to accurately hone blind bores which are bores that are open at one end but blocked at or adjacent to the opposite end. The present invention also relates to the method of programming and using the same apparatus for honing blind bores.